This invention relates to a process for economically producing absorbent board from peat moss and more particularly to a process for air laying peat moss to form an absorbent, flexible, strong board capable for use in such diverse products as body fluid absorbent products, e.g., sanitary napkins, dressings, diapers and the like, as well as in horticultural products, e.g., as a mulch for growing plants.
The use of peat moss, in combination with other fibrous materials, for absorbent products, has been suggested in several prior disclosures such as for example, U.S. Pat. Nos. 4,170,515; 4,226,237; 4,215,692; and 4,507,122. Additionally, processes have been suggested for incorporating peat moss into a fibrous board product, such processes exemplified by U.S. Pat. Nos. 751,139 and 4,473,440.
The latter cited U.S. Pat. No. 4,473,440 is particularly pertinent as it discloses a process for producing aborbent, flexible peat moss board for use in absorbent products. In accordance with the teachings of this patent, sphagnum peat moss is first screened to remove large materials such as roots and branches and to remove fine particles, i.e., those passing through a 100 mesh screen. The screened peat moss, optionally combined with other fibrous material, is then formed into an aqueous slurry having a solid content of from 0.1 to 1.0% by weight. The slurry is then flowed onto a Fourdrinier wire where it is dewatered to form a low density board. The board is dried to a critical moisture content and then calendered to provide a highly absorbent flexible peat moss containing board.
While, in the main, the product resulting from this prior art process is quite satisfactory for use in absorbent products, by following the teachings of this process certain drawbacks are encountered.
Firstly, the requirement of providing screened peat moss creates great economic burdens to the process. Because both large and small particles of harvested peat moss are discarded in the course of the screening, essentially only half the material handled during harvesting and screening is actually utilized in the product. Yet this fact notwithstanding, the process cannot tolerate large particles without grinding and certainly cannot tolerate small particles, i.e. peat moss fines, in that the Fourdrinier wire would quickly become blocked by such fine particles and soon render further efficient wet laying of board impossible. Thus, the efficiency, as measured by raw material usage, is poor.
Further, the wet laid process of the prior art requires that the board be laid from a very dilute slurry, dewatered on the Fourdrinier wire and then dried to the prescribed moisture level prior to calendering to produce the flexible absorbent board. As is evident, it is necessary therefore, to accomplish the drying of the peat moss at a point in the process after the board is formed, i.e., at a point in the process whereat drying is most difficult, entailing expensive drying equipment and great energy input.
Still further, because of the inherent limitations in a wet laid process, the choice of other fibrous materials to be combined with the peat moss is necessarily limited. Too fine particle sizes cannot be tolerated and other fibers, having relatively long length, become entangled in clumps and destroy the uniformity of the resulting product.
Accordingly, there is a need for an improved process for producing flexible, absorbent peat moss board.